"Grafting-to" Polymers of Xylan-g-allyl Glycidyl Ether Toughen PEG Hydrogel via Microphase Separation: Thermoresponsive and Photoreactive Molecular Assembly in DLP 3D Printing.

Utilizing naturally derived biopolymers in the macromolecular design of thermoresponsive polymers offers sustainable and biodegradable smart building blocks to functional materials. Here, a novel graft polymer of xylan-g-allyl glycidyl ether (xylan-g-AGE) that is thermoresponsive to self-assemble and photoreactive in photopolymerization is reported. This research highlights an innovative use of the debranched wood xylan, a chemically engineered linear polysaccharide of β-1,4-linked xylose, as the backbone in grafting polymer, which allows a greater degree of spatial coordination for sidechains than the analogous cellulose. Induced by the reformation of H-bonds and hydrophobic effect, xylan-g-AGE transits from solvated coil chain to self-assembled mesoglobules upon the temperature change above its lower critical solution temperature (LCST). When xylan-g-AGE is used in photoresins to fabricate hydrogels with good geometric fidelity via DLP 3D printing, solvated xylan-g-AGE stiffens the polyethylene glycol (PEG) hydrogel strongly, due to higher crosslink density of available AGE moiety and faster crosslinking rate, while self-assembled xylan-g-AGE toughens the PEG hydrogel better, attributed to the strategy of "dual chemically independent domains" that smartly combines tough domain of PEG and soft domain of self-assembled xylan-g-AGE. Conductive hydrogel is fabricated by incorporating 2D MXene sheets into this hydrogel matrix in DLP printing, which demonstrates superior performance as wearable strain sensors.